Albxahdeb geobge ca



sept. 1,1925.

E H T mun S T Fw DD AO ER LP GY WB N im MA N Low.;- LcE ES L l BE R PO 2 M l E A v. l C u J G .w n A F METHOD OF TREATING CRUDE SULPHID RECOVERY OF HYDRATED CARBONATE OF eriee.

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'To @il whom. it may cof/wem:

Be it known that LmANDer Gijre CAimBELL, e subject cf the Gre/ei', Britain, resifiing; et Broken Hiii, iii fue State of New South `Weies (crmeriy of Kie-0re Bay Road, Sandringham., in the Siete of Vic-toria), Commcnweelh ef ustrel'is, has invented certain new en. eseui improvements in improved methed ci ireeing crufie suiphide ores containing iea r che recovery of hydrated cerbcneeo iced and luy-products, of which the 'foiiowing is e specification. l

The present invention proviries for bile recovery of White leed and silver rom cree sulphide ores containing suiphides ef silver lee and zinc, or 'ccncentrees midlings or by products obtained rrcm *whe treement cf such ores.

It is the purpese of this invention oieeve 'die eine? ai; iie emi ci ehe process, in uneitered condition es 'i siphide.

it *che preserel; there ere yzmmerees inventions amd processes which reie'be 'Sine production of White leaciby what are mewri precipitation processes, heij is say, processes in which the iea is irse dissciveci in e soiuiiori such. as eceiic acid., or of 'eikeiiiie salt, er some ether solvent., ac

from which it is precipitated es e hydrated carbonate by various methods. ,Msc emcrig these precipitation processes there ere seme which make use of Well known eiectrcchemical reefcicns whereby an anode of rneiei'iic.

er pig leed is disseived by the aerien e. eiecric current passing through, e

eiectrolyte, while e caustic alkali .is pro duced the seme time the cetnoe., te "0e used., either directly or ind,irec'rly7 'te preeipitete Jche leed from its seiuiicn. 1in eil precipitation processes, Wiiether-the is isscvcd by er einer ineens the .:iiic iezw., invoking sind reiini etere of whife iiie it hiiieitc Le prcmuce i straniere by diseeii. A... me costly 'processes smell ef ief eres ceiere che iced is ever` cemmcncc e been 'found exirce'icijf c z product showing mi he iiicresccpe, which is e desirabe is the cf Seis invention ec produce e wiiie iced of goed que-.Hey by direct treatmen; ci e suipiiide ere, by hyrmmetallub gicei metheris. eliminating the expensive and unnecessary processes et present invoived in @ce preductien of metallic leed.

To erect iis e series o'tiree steps are invoivef wiiiel inciufie :u

First. ebjeei 1g the ore tc e@ process whereby fue ieeci and' siiver velues become coneineci es ciiieriiies in am alkali metal chioride schreien.

Seccndy. Treeeirig the soution for the eimineiori c1? impurities. Thircijv. Precipiieting the eed in Sciuicn es e iiydr raide, which is ihen converte 'to e nyairee carbone-ce of iced.

Aiificegi of reieed. steps is hereirm ceime-l iri combineion, certain iiec'ors crise wii be evident from he elicwing :iescripien which involve speciiie claims for c r'f mei-hos of perform 7 steps in the entire ing eii. or individu@ creetmerit.

Alec, in the cii vf/*ing description, it wil siiver emi e Wise be unpro'iabie fe extract, emi which because essceiete with zinc Woud have iitcsveue.

.irst of the ebove speeied materiel is first crushed and wee. subgecbed te Ae preferential whereby he leed and vsilver values are converted to chlorides While the zinc remains substantially unaltered as a sulphide.

There are already methods in existence whereby this object may be attained. Thus the material may be roasted, under suitable conditions of temperature and time, with chloridizing agents such as metallic chlo- Vrides or hydrochloric acid, Without the `presence of oxidizing agents, or Wit-h an alkali metal chloride such as common salt, in an oxidizingatmosphere.

In all these methods, when the temperature is maintained Within certain limits, the lead and silver values may be .chloridized Without affecting the zinc but there is a disadvantage which lies in the expense of a chloridizing agent.

As will be later described, my special and novel method of precipitation, used in this particular modification of the process, involves at the same time the production of an equivalent amount of chlorine, and for lthis reason the preferential chloridizing roast is carried out in the presence of chlorine. The ore, after having been crushed and ground, is roasted in an atmosphere of chlorineain a suitable furnace or heated containing vessel at such a temperature as to convert the lead and silver values to chlorides, but to leave the zinc sulphide unaltered. Now though successful chloridizing of the lead and silver may be done by this means, there is a loss of chlorine due to its leaving the furnaces as gaseous chlorides of sulphur, and to prevent this it is preferable to add moisture in the ferm of steam, and also air, to the furnace inosphere so that the chlorides of sulphur having been broken up by steam, the sulphur may be oxidized to sulphur dioxide gas.

In the treatment with chlorine as described it is essential that the temperature of the reaction be maintained Within ceri tain limits. This temperature will vary with.

different classes of ore and should be ascertained by direct experiment on a sample beforehand, but generally it has been found that a temperature of between llOO" C. and 500O is sufficient. Also the amount of steam added should be suflicient only to break up the chlorides of sulphur formed by the action of chlorine on the sulphides. On the other hand the air, to complete the oxidation of sulphur, may be added slightly in excess Without causing the formation of sulphates of either lead, silver or zinc. This method of preferential chloridizing of an ore by roasting, with chlorine to which steam and air -has been added differs essentially from methods using hydrochloric acid alone in that steam and chlorine are employed as reagents instead of hydrochloric acid, that any hydrochloric acid formed by the action of steam on chlorine or chlorides of sulphur play only a secondary part in trie reactie assenso the main reagent being chlorine itself, an oxidizing atmosphere present purpose of oxidizing the sulphu using hydrochloric acid alone. no agent is used at all, the gas linea sulphuretted hydrogen.

Suitable means l uld ne provided" ,in

D. roastingjto rabble ci' otherwise leep the inaterial in intimate contact with. the

gases.

rThe roasted ope is now Wash 1 Water, by which the bulli of iron, mangalpese and copy While the lead and silver chloi practically insolfuble remain unal These chlorides of lead and silver are now suitably leached, whereby' the bulk of the lead but only a small and variably amount of silver chloride, unless measures are taken to increase its extraction, as later described, is brought into solution.

This solution, however carefully the roast ed ore may have been originally Washed., will usually be found to contain small quai-- titles of impurities such as chlorides of iron, manganese or copper which must be remoi if a pure White lead is to be produced. At this stage the performance of the second` of above steps has now to be co'sidered. Since the lead is ultimately to be precipitated as a hydroxide, it is essential that no rea!Jr should be used to ecipitate impui Which Will itself torni a soluble salt will later be precipitated with and coi nate the White lead. For this reason precipitants used foikremoving the impurr ties must be either metallic lead, or salts of lead, or sodium salts or salts o'.Y2 some base which will produce a salt in the ion which may be precipitated itself by a sodium or lead salt, or by some acid. Thus the silver may be precipitated by the known` method of agitating the solution with grann ulated or sponge lead, whereby the lead and copper are precipitated in the metallic state. The lead 'with the deposit of silver and copper may be removed from'tiine to time smelted to produce a silver l l r lron may be removed by a i powdered lead carbone when 3 thrown down as an i" r ,l tate, or iron and c: j moved as insoluble sulp byagitation with powdered lead sulphide and this lead sulphide may be produced in the solution itself by a measured amount of sulphuretted hydrogen or a soluble sulphide such as sodium sulphide.

Iron and manganese together may be precipitated by suitable oxidizing agents such as red lead or lead peroxide.

ln eachV of these cases when lead or a lead salt is used as a purifying agent, `more lead chloride is kept hot'and brought into ist form of White lead so that -the expense of the cost of precipitants'is counterbalanced by an increase vin saleable product.

Both iron and manganese may also be removed fromtlie solution by selectively precipitating'them, with only a slight loss of leed, by addinor an amount of an alkaline hypochlorite slightly in excess'of the the-v oretical quantity required. A convenient lmeans of obtaining an alkaline hypochlorite for this purpose is to' agitata bleaching powder in the solution,'.in which case a certain amount of calcium` chloride is brought into solution., i

This may be precipitated, Without affect ing the lead, as an insoluble sulphate by the addition of an equivalent amount of sodium sulphate or lead sulphate or sulphuric acid.

to the solution.

In using any one ofthese methods of urification the precipitant must -be agitated y suitable means in the solution, which must be also filtered carefully after the reaction is complete.

In addition to the above methods of purication a pure solution of lead chloride in brine may be obtainedy lby crystallizing some of the lead by cooling, filtering, and

returning the solution for further leaching.

The crystallized lead chloride may then be washed in pure'water and re-dissolved in a separate brine circuit for further treatment.- l

The third of the above steps has now to be carried out.

The purified and hot solution of lead chloride in brine, after filtration, is passed into a suitable agitator or mixerwhere it is mixed with a solution of caustic soda, which, reacting With the lead chloride, throws down an insoluble White precipitate of lead hydroxide and produces atthe Sametime an equivalent amount of sodium chloride which thus regenerates the solution.

This precipitate may then be converted to a hydrated carbonate of lead by passing into it, While agitated, a stream .of carbonio acid gas, and this operation is best carried out in a closed containing vessel to avoid loss of gas7 the gas being introduced in measured quantity to supply Whatever proportion of carbonio acid gas as may beA desired. Generally the amount of gas introduced is equal to the theoretical amount given by the formula QPbCOBPMO/Hh, as White lead having this formula has been found to be of the best quality, but no particular amount is specified in this invention.

The process of introducing carbon dioxide gas into the precipitate may be carried out under pressure, in which case the reaction is more active, and it may also be carried out byirst filtering the hydroxide from the brine solution and then mixing it with Water in the agitator.

In precipitating the hydroxide from the brine solution by an alkaline metal hydroxide it has been found that a crystalline compound of the hydroxide with Water has been apt to form, and that this combined water, after treatment of the precipitate with can bonic acid gas, is diiiicult to drive oit When drying by heat. i

This formation of crystalline compounds has'been foundto be minimized by carrying out the precipitation in a solution which is heated to a temperature which will vary slightly according to its strength, and is best found by direct experiment, although satisfactory results have been obtained with a number of solutions or' varying strengths at 75C.

The precipitated hydrated carbonate of lead, after careful Washing and filtration, is slowly dried and is then in a condition 1to dbe ground in oil as commercial White This precipitate, obtained under these conditions, has been found' to be equal in urity of color, 'covering power and amorp ious structure with White lead made by the stack process.

The hydroxide of lead, formed by precipitation by a caustic alkali, may if desired be converted to a sulphate by digesting or heating with sulphuric acid, and. this -sulphate may be used as a pigment. Lead sulphate however, has only one advantage in being nonpoisonous, While the hydratedcarbonate, although a poisonous compound,

has a greater spreading and covering power "seen that the process is completely' regenerative, the only agents to 'be purchased being lectrical power, sufiicient Water to malte up the amount lost in the form of lead hydroxide, andsalt to make up unavoidable losses in Washing, etc. It'must also be pointed out that as a solution ot caustic soda and brine is only required here, the usual costly procceses in manufacture ot caustic soda, ofyp'roducing a solid product tree .trom moisture and salt is dispensed with. i

'Though the method which has non7 bee described has been found, for the reasons ico already given, to be economically the most suitable for carrying out the three steps mentioned above, it is not intended that it shall be binding to exclusion of other vmethods ot carrying out the individual steps.

Thus silver and lead may be obtained as chlorides in an alkali metal chloride solution by other means, such as by known wet methods, and the lead precipitated from the purified solution by some alkaline hydroxide such as ammonium hydroxide which will precipitate the lead but not throw. down 'the base of the chloride used as a solvent.

Of available hydroxides it has been found that lime is so slightly soluble and has such a tendency to torni oxychlorides of lead that it is impracticable, while potassium is usually too expensive.

Ammonium hydroxide may be used with cold solutions, to prevent its breaking up by heat, and may be recovered from the leach solution, after filtration of the precipitate, by digesting while heated with lime, the fumes ot ammonia, given olf being collected for further use, while the solution gains an equivalent increase in calciumchloride.

This method involves the use ot large volunies of solution, as calcium chloride has a lower solvent power of lead chloride than brine especially when cold while it is diliicult also to avoid losses of ammonia.

It will thus be seen that, provided power may be obtained at a reasonable cost, the particular method detailed, that is the use of a brine solution and caustic soda as a precipitant, has the greatest advantages.

It will also be obvious that there may be occasions, when dealing with certain ores, there will be no necessity for purifying the leach solution, but the elimination of this 'step does not necessarily alter the principle of this invention.

ln the leaching of the roasted ore it has been found that however well the silver val ucs may have been chloridized, that only a small amount mav be brought into solution owing to the tact that being in contact with Zinc sulphide it rcverts itself to a sulphide.

This difficulty in leaching silver in the presy ence of unaltered zinc sulphide hasl been known for a long time and various mechani cal methods have been devised to overcome it, the principle being to remove the silver chloride, when once in solution, as soon as possible-'trom contact with the Zinc sulphide by such methods as rapidly passing the solution through the beds of ore on filter beds, 0r by the use ol' suction ilters or centrifugal extractors or the like.

These methods have all a fundamental disadvantage in that the silver is only removed ater it has dissolved and is so in a state in which it can. react with the zinc sulphide and a special method according to this invention will now be described Wherey Matese by the silver and lead chlorides are largely removed from contact with the zinc sulphide before being dissolved at all.

This method consists in pouring a stream ot' roasted ore on te the surface of a nievingstream of leach solution so that the particles of zinc sulphide, sinking at a faster rate than the particles of chlorides, are rapidly and simply removed from Contact with the silver in solution. The attached sectional elevation will shew a simple and convenient means by which this can be effected, the description being as ollowwm- (l) is a small hop-per into which the washed ore is placed and by means of a spray of hot brine from the pipe (2) is washed in a thin stream on to and across the surface the solution in the leaching trough The het leaching solution is introduced into this trough by means of the pipe (3) and by the perforated-bams is distributed evenly. rlhis stream of het solution ows through the trough as sheWn by the arrows, to the perforated baille (6) and' then out of the trough by the pipe (7).

l/Vhen the washed orc :flows on to the surface or the leach solution the particles of zinc sulphide sink evenly through the solu tion and more vquickly than the particles of chlorides. These becoming smaller and smaller as they dissolve, sink more and more slowly so that by tlielgtime the Zine sulphide has fallen to the bottom the operation is complete and the chloijides leave the trough dissolved in tlie solution.

The Zinc sulphide residue is removed by the plug holes 8, while the depth of low of solution may be controlled by covering the pertorations in the bullies by means of the slats fixed in. grooves, one of. which is shewn in the diagram at the exit.

By this means a higher extraction of silver may be obtained than by other mechanical 1nethods, while the time and enp'ense of the operation is largely reduced. As an alternative method of recovering the silver, the ore may be. leached iirst `for lead and the silver afterwards leached from the zinc residue by known solvents which will dissolve silver sulphide, such as a solution of a double hyposulphite o't sodium and copper,y or by chlorine in a brine solution, or by a solution, containing a metal forming higher and lower chlorides and saturated with Vchlorine.

As an example of the use of chlorine for the preferential roasting el' a silver-leadzinc ore, a sample of 'silver lead zinc reiddlings assaying 25.8 oa. silver, 86.8% lead, 24.7% zinc was roasted in an atmosphere ofchlorine fora period of one and a half hours, at a ,temperature not exceeding 450 centigrade. The roasted material was then. leached with known solvents when the residue was found to assay :2.9% lead.'

In each case the zinc sulphide was found to.

be substantially unaltered.v

I claiinrl. A method for the production of White lead from crude ore or` concentrates containing lead, by first chloridizing the silver and lead values and then leaching these values by a solution of an alkali inetal chloride, secondly purifying this solution, and finally precipitating the lead as a hydrated carbonate by the addition of an alkali metal hydroxide followed by agitation with a Stream of carbonio acid gas.

2. Producing white lead from crude ore or concentrates, by a preferential roast with chlorine, leaching the lead and Silver chlolrides by a solution of brine, purifying this solution7 and precipitating the lead as a hydrated carbonate by meansoic caustic soda and carbonio acid gas. i

Dated this 16th day of May 1922.

ALEXANDER GEORGE CAMPBELL. 

